Linear low-density polyethylene (LLDPE) is made from or contains ethylene/α-olefin copolymers containing an amount of α-olefin deriving units for yielding a density in the range 0.88-0.925. These copolymers are useful in the field of wrapping and packaging of goods, including stretchable films. In some instances, LLDPE is produced with liquid phase processes (solution or slurry) or gas-phase processes. Both types of processes involve the use of Ziegler-Natta MgCl2-supported catalysts. In some instances, the catalysts are formed by the reaction of a solid catalyst component, in which a titanium compound is supported on a magnesium halide, with an activator such as an alkylaluminum compound.
It is believed that having a comonomer randomly or alternatively distributed along the polymer chain and, at the same time, having the polymer fractions with a similar average content of comonomer (narrow distribution of composition) may provide high quality ethylene copolymers. These latter can combine, at the same time, a density low with respect to HDPE and a low content of polymer fractions soluble in hydrocarbon solvents like hexane or xylene that may worsen certain properties of the resulting copolymers.
In some instances, certain Ziegler-Natta heterogeneous catalysts are based on Ti compounds supported on magnesium chloride further containing a certain amount of cycloalkyl ether as internal electron donor. In some instances, the cycloalkyl ether is tetrahydrofuran (THF).